Some internal combustion engines are equipped with electric valve actuators that can be operated to vary the position of an intake or exhaust valve of an engine cylinder. Some electric valve actuators may include a spring that biases the valve at a particular equilibrium position. In order to move the valve relative to the equilibrium position, a current may be supplied to a magnetic coil of the actuator. In some conditions, a minimum or base level of current may be applied to the actuator to hold the valve in a particular position away from the equilibrium position. However, identifying the base level of current for a valve may be difficult due to variations in valve construction and/or changing operating conditions of the valve. Likewise, individually testing each actuator before installation may be impractical or costly.
In one approach, a common level of current for some or all of the electric valves of a set may be identified by determining the highest base current or upper limit of the tolerance of all of the electric valve actuators of the set. The common level of current may then include at least the highest base holding current of the set and may include an additional amount of current to provide robust operation.
However, the inventors herein have recognized that some issues may exist with the above approach. Specifically, a common holding current delivered to two or more valve actuators may result in a higher level of current than is necessary for some of the actuators to maintain a particular holding position. This additional current supplied to the actuators may serve to increase the power consumed by the electric valve actuation system, during some engine conditions. Further, differences between the base level of current for holding the valve actuator and the assigned common level of current may cause variations from actuator to actuator in the time delay between a valve command and physical movement of the valves. These variations in response time may, in at least some cases, degrade engine performance or efficiency.
In a first approach, as described herein, the above issues may be addressed by a method of operating an engine including at least a cylinder and a valve controlled by an electric valve actuator, said actuator including at least a coil and an armature moveable thereto, said armature coupled to said valve, the method comprising moving the armature toward the coil by varying an amount of current supplied to the coil in response to a location of the armature relative to the coil; identifying a first level of current supplied to the coil at a first position of the armature during said moving the armature toward the coil; and holding the armature at a second position relative to the coil by supplying a holding current to the coil, wherein said holding current is adjusted to be less than said first level of current.
In this way, a valve actuator may be operated at or near its particular base holding current in response to a condition of the valve system during operation, for example, during soft landing operation. Note that this approach may be applied during operation of the valve or during a pre-operational state of the valve, such as prior to start-up of the engine or cylinder.
In a second approach, also described herein, the above issues may be addressed by a method of operating an engine including at least a cylinder and a valve controlled by an electric valve actuator, said valve including one of an intake or an exhaust valve, the method comprising varying a first level of current supplied to the actuator to cause a corresponding change in a position of the valve; supplying a second level of current to the actuator during a subsequent holding operation of the valve based on a time delay between said varying the first level of current and said corresponding change in the position of the valve.
In this way, a valve actuator may be controlled using a holding current that is based on a time delay experienced by the actuator during operation of the valve. Note that this approach may be applied on an individual actuator basis among a plurality of valve actuators of the engine.
Further, the first and the second approaches described herein may be used together or independently to reduce power consumption of the electric valve actuation system and/or to reduce delay variance between valves. Still other approaches described herein may be used to provide a sufficient holding current while reducing delay variations among valves and increasing efficiency of the valve actuation system.